Such pieces of X-ray apparatus are used for intraoral photographing of teeth and oral tissues. In such apparatus, the X-ray apparatus itself is enclosed in a housing which is mounted on gimbals, and the housing has a protruding cone, which will lead the bundle of rays from the X-ray tube against the object which is to be photographed. A plate is placed in the mouth of a patient and the housing is directed in such a way that the rays will hit the plate. In the majority of cases, the patient will hold the plate. This is a drawback, partly because a picture of the patient's finger may disturb the taking, and partly because the plate has a random orientation in relation to the rays. These conditions entail that several photographs may have to be taken before a desired picture is acquired, which results in the drawback that the patient may be exposed to too large doses of X-rays. It is desirable to obtain the desired picture through only one operation, and furthermore, it is desirable for the picture taken to have a certain and standardized orientation in relation to the mentioned protruding cone. If this is the case, and the picture is sent for examination, each dentist who is to interpret the picture will know how the plate was placed in proportion to the X-ray tube when the picture was taken.
In U.S. Pat. No. 3,473,026 it has been proposed to place a ring loosely round the protruding cone, which can hold a bar, which has an axis that substantially coincides with the axis of the cone. The bar has a part which forms an angle with the longitudinal direction of the bar and whereat an X-ray plate has been fastened. This well-known device is difficult to orientate, and in connection with each picture-taking operation it must be placed upon the X-ray cone. Furthermore, the apparatus has the drawback that the bar complete with holder, after taking of pictures of different patients, must be completely replaced by another bar complete with holder. Furthermore, the desired standardized orientation of the plate in relation to the X-ray cone is not acquired.